Thread: Took a run with the tune and watched some aerofroce parameters...

Originally Posted by FriboRage

Everything seems alright driving around, it runs about 20* timing advance at/near wot... Longterm Trim B1 (which I assume is LTFT) went around -2 to -3.5 at/near wot.

Something I dont quite understand is negetive and positive in ltft cause some places I see people talking about positive and some places I see negetive... but anyway that's what my aeroforce was displaying, 0 KR the whole time.

Something that made me say 'wtf' was, after I let off the gas on my wot run, I was cruising about 70mph with little throttle, and my ltft went wayyy up to -23.4, I thought it couldnt go higher than 16.4? Does negetive mean something different? This is what I mean about the confusion on negetive vs positive fuel trims.

LTFT shows what kind of adjustment or "trimming" the PCM is making. When the numbers are positive that means the PCM is adding "+" fuel and when the LTFT are negative the PCM is taking away fuel. (-)
So right after you went WOT and took your foot off the pedal you didn't need all that fuel anymore so the PCM pulled a bunch which gave you your -23.4

Originally Posted by FriboRage

Ok, that makes some sense... so when it's say going between -5 and -10 under normal driving conditions... you say it's taking away fuel, but like... What is it subracting fuel from? Like how much the injectors are spraying each cycle? what does the condition of zero represent? and what units is that measured in? -23.4... what?

Also, how does LTFT differ from Short Term Fuel Trim?

Sorry Im full of questions trying to figure this out, lol.

Yes any time your LTFT show negative the PCM is taking fuel away(telling the injectors to spray less), you can scan your IPW's(injector pulse width) to see what the injectors are doing.
-23.4 is what you said your LTFT's read after you lifted from WOT so why are you asking -23.4...what?
You can't remember what you wrote...or what? LOL

Originally Posted by FriboRage

No, I just mean... 23.4 is an amount, what is the units the amount is measured in... like when you say timing is 20... it's twenty degrees, not just 20.

like -23.4 lbs/minute or whatever the rate injectors are rated at?

It's a percentage of fuel thats being taken away or added.

Originally Posted by FriboRage

And as my final question for the night... what would zero be since nothing is being taken away or added? Like what is the starting point to add or subract from?

I think I remember reading somewhere that zero is ideal at wot... and Im not 100% sure but before I got my tune my ltft's were always in the positive, now they're always negetive...

Ok Im done now

Between -5 and + 5 on the LTFT's is a good place to be and locking in at zero during WOT is ideal.Zero means just that, zero fuel is being taken away or added at that time, remember the PCM makes these changes based on the tune and the values the o2 sensor is reading. Alot of "canned" tunes will err on the rich side for safety,which may be why you've seen the slightly negative LTFT's since the tune. An in car street tune is best for getting the tune dialed in perfectly to suit "your" car.